"git worktree" learned move and remove subcommands.
* nd/worktree-move:
t2028: fix minor error and issues in newly-added "worktree move" tests
worktree remove: allow it when $GIT_WORK_TREE is already gone
worktree remove: new command
worktree move: refuse to move worktrees with submodules
worktree move: accept destination as directory
worktree move: new command
worktree.c: add update_worktree_location()
worktree.c: add validate_worktree()